Pocket Disassembler is a frontend to libopcode in GNU Binutils which lets you disassemble individual instructions for many different architectures, including ARM, x86, and PPC. Pick your architecture, type in the hex, and hit the button, and you get the disassembled instruction.

Erasm++, the Embedded Runtime Assembler in C++, is an Embedded Domain Specific Language (EDSL) in C++ for runtime code generation on Intel 64/IA-32 architectures. It supports complete compile-time syntax checking, and its code generators run very quickly because necessary data are computed statically. Also included are GenericDsm, a fast and generic instruction decoder library which supports "pattern matching" against the decoded instructions, and MetaPrelude, a Haskell-like lazy metaprogramming library that helps implementing EDSLs in C++.

Bokken is a GUI for the Pyew and Radare2 projects. It provides an interface to almost all the features of Pyew, and many in radare2. It's intended to be a multi-architecture disassembler and binary analysis tool, and maybe some day an alternative for commercial alternatives as IDA Pro. Currently, Bokken is neither a hexadecimal editor nor a full featured disassembler, so it should not be used for deep code analysis or for modifying files.

Opdis is a wrapper for the libopcodes disassembler library distributed as part of GNU binutils. It extends the libopcodes library by offering linear and control-flow disassembly algorithms, instruction and operand objects that are suitable for analysis, and a command-line utility to perform disassembly on arbitrary locations in a file. The Opdis project consists of the libopdis library and the opdis command-line utility. There is a Ruby gem providing access to libopdis, and a supporting gem providing access to libbfd.

jdisasm.py is a Java class file disassembler. It displays a Java .class file in a human readable form, showing the class name, the field names and types, and the method names, types, and codes (including instruction mnemonics). For each item shown, the file offset is prepended.

PostSharp is a tool for .NET and Mono developers.
It can reduce the number of lines of code and
improve its logical decoupling. Therefore, it
helps you deliver higher stability, cleaner
design, and cheaper source code maintenance.

minibug is a simple two-window debugger for
assembler programs. It runs in the console or X
terminal. It reads ELF executables and extracts
any symbols or comment information. Registers,
breakpoints, memory, and disassembly are displayed.